Method for producing shale oil from an oil shale formation

ABSTRACT

A method for producing shale oil from a permeable zone formed within a subterranean oil shale formation by circulating through a well borehole in contact with said permeable zone a fluid containing at least one phenolic compound.

IPTQIZ XR 395939790 --|l"\- vuuvwu l. twill, [H] [72] Inventor John A.Herce 2,288,857 7/1942 Subkow 166/275 X Houston, Tex. I 2,365,59112/1944 Ranney 166/272 X [-21] Appl. No. 789,089 2,859,818 11/1958 Hallet a1. 166/271 X [22] Filed Jan. 2, 1969 3,221,813 12/1965 Closmann etal. 166/272 X M 1 1 Palemed J y 1971 3,241,611 3/1966 Dougan 166/272 X[73] Assignee Shell Oil Company 3,322,194 5/1967 Strubhar.... 166/272 XNew York, 3,358,756 12/1967 Vogel 166/272 X 3,392,105 7/1968 Poettmannet a1 208/1 1 6 47 [541\METHODFORPROWCINGSimon-WOMAN 3331223 13113233223,; m1. mkizix OIL SHALE FORMATION 6 cu 3 D i Fi Primary Examiner-IanA. Calvert 52 us. Cl 166/267, "omeyhmms and Mccanhy [66/271, 166/272,[66/275, 166/303 [51] Int. Cl E2lb43/22,

E21b 43/24 [50] Field of Search 166/247, 1

265, 267, 2.63, v 275, 303; 1 ABSTRACT: A method for producing shale oilfrom a perme- 1 References cited able zone formed within a subterraneanoil shale formation by circulating through a well borehole in contactwith said UNITED STATES PATENTS permeable zone a fluid containing atleast one phenolic com- 2,267.548 12/1941 Berl 166/275 pound.

OIL

SEPARATOR PATENTED JUL20 I97! HEAT EXCHANGER SEPARATOR "LI I 5 FIG. 3

INVENTORZ J. A. HERCE BY. f ga a FIG. I

HIS ATTORNEY METHOD FOR PRODUCING SI'IALE OIL FROM AN OILL SHALEFORMATION BACKGROUND OF THE INVENTION 1. Field of the Invention Theinvention relates to a process for solvent extracting shale oil from asubterranean oil shale formation; more par ticularly, it relates to aprocess for recovering shaleoil from a permeable zone in an oil shaleformation by circulating therethrough at least one phenolic compound.

2. Description of the Prior Art Shale oil as kerogen, which is abituminous material present in oil shale formations, can be removed fromoil shale by pyrolysis at elevated temperatures. A big drawback tothere? torting of oil shale to recover shale oil is the need to removeand dispose of a substantial amount of the shale after it has beenretorted. In viewthereof, in situ retorting has found much favor inrecent years as a method of recovering shale oil, g

particularly from subterranean oil shale formations. One such method isto create alarge, permeable zone within the oil shale formation byrubblizing such a zoneby an explosion within the formation, e.g., byutilizing high-energy explosives such as nuclearbombs. One or moreaccess wells are then drilled .into the fragmented zone andcommunication is establishedbetween the permeable zone and openings intothe wells. Hot fluids are then injected, usually to startan in situcombustion heating process which causes the shale oil (kerogen) tobecome fluidized. The shale oil is then recovered from a production wellby conventional means.

SUMMARY OF THE INVENTION It is an objectof this invention to produce.shale oil froma subterranean oil shale formation more efficiently thanhas been previously accomplished.

It is a further object of this invention to improve the rate ofrecovery, amount of recovery and/or the nature of the petrole ummaterials. that are recovered from a subterranean oil shale. formationby use of at leastone phenolic compound havingunique oil-extractingproperties.

These objects are accomplished by extending at' least onewell bore holeinto a permeable zone formed within a subter ranean oil shale formationand circulating an aromatic organic Bronsted acid, such as a phenoliccompound therethrough per: se or in a fluid carrier. Shale oil andcirculating extracting fluid:

material are then recovered from the permeable zone. and-theshale oil isseparated from the extracting material. The forma? tion should bepreheated prior to injection or the circulating; fluid should-beinjected hot in carrying out this process. By aromatic Brgnsted acid" ismeant an aromatic substance that loses a proton as defined in AdvancedOrganic Chemistry,'-.. pp. 491-2, by Fieser and Fieser (I961 Insituations in which it is desirable to mine portions of an oil shaleformation and pyrolyze the mined oil shale in afluid heated, pressuretight, surface located'retort, the pyrolytict recovery of petroleummaterial is improved by incorporating an effective amount of phenolic.compound in the hot fluid:

benzene solution of a phenolic compound, theoilshaleis preferablypreheated by contacting it with' hot aqueous liquid. The contacting ofchunks of oil shale with a hot aqueous liquid, (i.e., with hot waterutilized in preheating the oil'sh'ale and/or a hot aqueous solutioncontaining at least one phenolic compound) tends to exfoliate the piecesof the oil shale. The exfoliation reduces the tendency for :clinkers tobe formed during the pyrolysis-extraction operation and: reduces theextent to which the oil shale needs to be crushed in order to obtain anefficient recovery of petroleum material.

BRIEF DESCRIPTION OF THEDRAWING FIG. I is a vertical sectional view ofan oil shale formation to which the. recovery process of this inventionhas been applied, involving a single-well borehole;

FIG. 2 is a vertical sectional view of the oil shale formation of FIG; 1wherein a pair of well boreholes are disposed in accordance with theteachings of my invention; and

FIG. 3 is a vertical sectional view of an alternate recovery process ofthe invention applied to the single-well borehole of FIG. I.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Referring to the drawing,FIG. I- shows a well borehole 11 extending into subterranean oil shaleformation 12. Fluid communication may be established between points 13and 14 in oil shale formation 12 and adjacent to borehole 11 along avertical fracture by, for example, a conventional hydraulic fracturingprocedure. Hot, aromatic Brglnsted acid such as a phenolic compound orfluid containing such acid is then circulated through tubing 17 pastpackers l8 and 19, or the formation should be heated and the fluidinjected, until oil shalederived fluidizable materials are entrained inthe circulating fluid; The fluid passes through perforations 20 and 21in casing 22. Of course, if the wellbore 11 is uncased, suchperforations are unnecessary. The fluidizable materials may then berecovered from the outflowing portions of the circulating fluid by anyknown means. Thus, a single well may be used, although itis generallypreferred to use at leasta pair of wells. As-seen in FIG. I, if a singlewell is used, thepreferred two points may be a pair of substantiallyvertically separated points that are apt to be encountered by verticalfractures within the oil shale.

As shown in FIG. 2, a pair of wellbores 23 and 24 extend intosubterranean oil shale formation'25. Fluid communication is establishedbetween point 26 adjacent to wellbore 23 and point 27adjacent towellbore 24. In a-preferred embodiment, the depths of such points may bethose at which a tuffaceous streak is encountered by a pair of wellboreholes between which the streak is continuous. The permeable channelextending through the oil shale may be formed by the process of locatingand acidizing a tuffaceous streak as described in an application Ser.No. 619,259 filed Feb. 28l967'to Prats, now US. Pat. No. 3,481,398. Ahot phenolic compound, such as as aromatic Bngnsted acid or a fluidcontaining the acid, is then circulated through tubing 29 past packer30, until the oil shale-derived fluidizable materials are entrained inthe circulating fluid. The circulating fluid passes through perforation31 in the casing 32 of wellbore 23, through points 26 and 27, andthrough perforation 33 in the casing 34 or wellbore 24. Again, if thewell is uncased, such perforations are unnecessary. Fluidizablematerials which are derived from the oil shale can then be recoveredfrom the circulated fluid by any known means.

The circulation of the hot fluid may be a long duration heatingoperation, and,.for some time, the amount of oil production may beinsignificant. The temperature of the circulating fluid is preferablymonitored either at the point at which the fluid flows out of thepermeable path or at the wellhead.

Oil shales aregenerally impermeable. Once a permeable path has beenestablished between a pair of wells, the permeable path will providesubstantially the only zone that can be penetrated by a fluid injectedinto either of the wells. In view of this, relatively simple equipmentcan be utilized to circulate the heated fluid through the permeable pathbetween the selected points. The fluid can be'pumped through a heatingdevice, through the permeable path, through a temperaturemonitoringdevice, and then recycled back through the heating device. Thedurationof the heating that is necessary for a given oil shale can be determinedby maintaining a sample of the shale at an equivalent temperature for anequivalent time until a suitable degree of conversion is obtained. Thiscan be done prior to or while circulating the fluid.

In FIG. 3, an alternate recovery process, which can be operated with asingle well, is illustrated. Here, the permeable channel formed withinoil shale formation 12 is preferably a relatively voluminous permeablefragmented zone 35. The term permeable fragmented zone" refers to amultiply-fractured zone in which the number of the fractures and thevolume of the interconnected openings within the fractures provide avoid volume of from about to 40 per cent of the volume of the zone.

Permeable fragmented zones can be formed by known hydraulic and/orexplosive techniques for fracturing subsurface earth formations. Onesuitable fracturing technique was described in I922, in US. Pat. No.1,422,204. The streak acidizing procedure of application Ser. No.619,259, filed Feb. 28, I967 which matured as US. Pat. No. 3,481,398 onDec. 2, 1969, may be used, preferably to form a channel into which aliquid explosive is injected and subsequently detonated to form agenerally disc-shaped permeable fragmented zone. High-power explosives,such as those produced by nuclear devices, are particularly suitablemeans for forming such fragmented zones. In general, the permeablefragmented zone formed by a nuclear device has a vertically extensiveand generally cylindrical shape.

In circulating hot fluid through a permeable fragmented zone, the flowpaths can be vertical or horizontal and can involve a radially expandingor line-drive type of displacement of the fluid that is circulatedthrough the oil shale. Generally, a substantially vertical downward flowis preferred.

FIG. 3 illustrates a portion of a nuclear chimney type of permeablefragmented zone 35. In treating such a zone, one or more wells 36 aredrilled to near the bottom, preferably while the zone is hot, or atleast warm, from the explosion energy. In the illustrated arrangement ofFIG. 3, the well 36 is drilled and cased to near the bottom and thecasing 37 is perforated at 38 and 39 and equipped for injecting fluidthrough the borehole annulus above packer I8, and through perforations38 into the upper portion of the fragmented zone. Fluid is produced fromnear the bottom of the zone through perforations 39 and tub ing string40.

With such an arrangement, the pressure within the permeable fragmentedzone is adjusted to one selected for the circulation of heated fluid.The adjustment is affected by controlling the rate of withdrawing fluidfrom the cavern relative to the rate of injecting fluid into the cavern.As indicated in FIGS. 1 through 3, conventional equipment andtechniques, such as heater 41, pump 41a, separator 42 and heat exchanger43 may be used for pressurizing, heating, injecting, producing, andseparating components of the fluid that is circulated through thepermeable zone 35. The production of the fluid can be aided by downholepumping means, now shown, or restricted to the extent necessary tomaintain the selected pressure within the zone. The pressure in the zoneis preferably maintained at a level suited for economically transferringheat into the zone by circulating a fluid that is economically availableat the well site.

A wide variety of aromatic Brgnsted acids and fluids containing suchacids may be used in this process. The main requirements are that theseacids be pumpable at a moderate temperature such as from about 400 to600 F. Carriers for the aromatic Brgnsted Acids can be oil-immisciblefluids such as water; aqueous liquids; steams of various grades, such alow quality steam, dry steam or supersaturated steam; or oil misciblefluids such as relatively low-cost volatile hydrocarbons that contain orconsist essentially of volatile oil shale hydrocarbons that contain orconsist essentially of volatile oil shale hydrocarbons may be used. Theaqueous fluids, e.g., water, should be softened to inhibit scaling atthe temperatures to which they are heated.

In certain situations, it is advantageous to circulate a mixture ofrelatively low-molecular weight, predominantly arematic hydrocarbonshaving relatively low critical temperatures and pressures. With suchhydrocarbons (which may include significant proportions of shale oilhydrocarbon) the temperatures and pressures within the permeable zonemay provide conditions approaching or exceeding the critical conditionsfor part or all of the circulating hydrocarbons. In the critical orsupercritical region, such hydrocarbons have densities and viscositiesthat are intermediate between their gas and liquid states and areparticularly effective in extracting organic components from oil shale.

In a preferred feature of my invention, an aromatic Brjzjnsted acid, areactive petroleum-extracting material having unique properties, isadded to the fluid being circulated through the permeable oil shaleformation of FIGS. 1 through 3 in an amount as low as about 10 per centby volume of the injected fluid. The reactive material may be mixed witheither an oil-immiscible or an oil-miscible fluid. The reactivematerials also include phenolic or substituted phenolic compounds, e.g.,phenol or cresol, which are relatively soluble in either oil or water.In the preferred method of my invention disclosed herein, the reactivematerial containing circulating fluid may contain the reactive materialeither as a solute and/or a separate fluid phase that is introducedeither continuously or intermittently into the well boreholes of FIGS. 1through 3.

EXAMPLE It has been found that the addition of a phenolic or substitutedphenolic compound to a fluid (e.g., water or benzene) circulatingthrough a permeable oil shale formation results in the extraction ofsignificant amounts of organic matter from the oil shale within the oilshale formation. Recoveries of percent Fisher Assay have been obtainedwith such phenolic compounds in much shorter time periods than knownprior art processes, as for example the process disclosed in applicationSer. No. 656,8l5, filed July 28, l967to Deans et al. which matured asUS. Pat. No. 3,474,863 on Oct. 28I969in which shale oil is produced bycirculating a volatile, normally liquid oil solvent through a permeablefragmented zone within a subterranean oil shale formation undersupercritical conditions of temperature and pressure. In the Deans etal. application, it was found that the addition of a normally liquidhydrocarbon solvent, such as benzene, to the circulating fluid gaveresults far superior to known prior art processes. Solvent extractionsutilizing aromatic Brgnsted acids, e.g., phenol or cresol, have achievedmuch greater recovery of oil than benzene solvents. For example, in aneight day period, I20 percent Fisher Assay was extracted by thecirculation of pure phenol. Under very long solvent oil shale contacttimes, recovery by the circulation of phenol still attained 120 percentFisher Assay. The phenol solvent may be recovered by conventionaldistillation methods yielding both pure phenol to be recycled back intothe oil shale formation and an organic enriched phenolic liquor.Further, a phenolic compound miscible in water may be dissolved in waterand then flowed through the permeable oil shale formation. Tests haveshown that phenol-water solutions of from about 25 percent phenol 75percent water effectively recover the shale oil (kerogen) from oilshale. The phenol water mixture of this method is sufficiently acidic toattack the carbonates which form a portion of the inorganic matrix ofthe oil shale within the oil shale formation. These acid attacksincrease the permeability of the oil shale and lessen the resistance ofthe oil shale to the circulating fluid.

The Fisher Assay method is a standard analytical method used todetermine the richness of an oil shale. The results are commonly givenin gallons of shale oil per ton of oil shale. Since this method isessentially a retorting process, much of the organic matter in the oilshale is converted to gas and approximately 20percent of the kerogen isleft in the residue as fixed carbon. Thermal solution processes, such asdisclosed herein, on the other hand, may be carried out at much lowertemperatures and more organic matter may be recovered without coking it.Therefore, recoveries by a thermal solution process, in accordance withthe teachings of my invention,

' resulting in a Fisher Assay greater than I00 percent are notanomalous.

Although good results in accordance with the teachings of the presentinvention have been obtained with phenolic or S substituted phenoliccompounds, any suitable aromatic or ganic Brg nsted acid having anactive hydrogen proton may be used with varying degrees ofeffectiveness. Examples of such organic compounds include: phenol,cresol, catechol, resorcinol, aromatic carboxylic acids, substitutedaromatic carboxylic acids, etc.

The use of aromatic organic Brgnsted acids, such as phenol hydrogen ionsattack the acid-soluble inorganic components of the oil shale, causingincreased permeability and solution of the inorganic matrix material.The active hydrogenions may also attack particular functional groupscontained in the kerogen molecules in the oil shale by breaking suchmolecules into smaller fragments more amenable to solution. Theremainder of the active hydrogen donor molecule, after donation, isemployed both as a solvent for the kerogen fragments and asa-transportation medium for bringing the fragments to the earth'ssurface. Finally, the entire process may take place at elevatedtemperature (namely above 400 F.) and pressure conditions, but theseconditions must be such that the solvent employed exists asa liquid.

I claim:

1. In a method for producing shale oil from a subterranean oil shaleformation comprising the steps of:

forming a permeable zone within a subterranean oil shale formation;-

extending at least one well borehole into the permeable zone within saidsubterranean oil shale formation; circulating a hot fluid containing anaromatic Brpnsted acid through said permeable zone;

recovering shale oil and a fluid containing said aromatic Brgnsted acid;and separating the oil from the fluid containing said aromatic Brgnstedacid.

2. The method of claim I, wherein the Brgnsted acid is a monomericphenolic compound.

3. The method of claim 2 wherein the monomeric phenolic compoundcomprises about l0 percent by volume of the circulating fluid.

4. The method of claim 2 wherein the step of circulating a fluidcontaining at least one phenolic compound therein includes the step ofintroducing said phenolic compound continuously into said permeable zonewhile said fluid is being circulated therethrough.

5. The method of claim 1 wherein the circulating fluid is watercontaining phenol. I

6. The method of claim 1 wherein the circulating fluid is anoil-miscible fluid containing phenol.

2. The method of claim 1, wherein the Bronsted acid is a monomericphenolic compound.
 3. The method of claim 2 wherein the monomericphenolic compound comprises about 10 percent by volume of thecirculating fluid.
 4. The method of claim 2 wherein the step ofcirculating a fluid containing at least one phenolic compound thereinincludes the step of introducing said phenolic compound continuouslyinto said permeable zone while said fluid is being circulatedtherethrough.
 5. The method of claim 1 wherein the circulating fluid iswater containing phenol.
 6. The method of claim 1 wherein thecirculating fluid is an oil-miscible fluid containing phenol.